Innovative solutions for carbon capture and utilization are required to achieve carbon neutrality. The electrochemical reduction of CO₂ (CO2RR) offers a promising approach for converting CO₂ into valuable chemicals and fuels. However, improving the performance of this process requires the design of active, selective, and stable electrocatalysts. Atomic layer deposition (ALD) is an advanced technique that enables the precise and conformal deposition of electrocatalysts on complex substrates, such as gas diffusion layers (GDLs).

In this study, ZnO gas diffusion electrodes (GDEs) were fabricated via ALD onto carbon-based GDLs. The growth parameters were systematically optimized at a fixed deposition temperature of 160 °C by varying the pulse times of the diethyl zinc and water precursors, as well as the N₂ purge duration. Spectroscopic ellipsometry performed on Si(100) substrates revealed a linear growth rate of 0.18 Å per ALD cycle, confirming the accurate thickness control.

Scanning electron microscopy showed that the electrodes had rough, crystalline surfaces with multi-faceted, flower-like structures aggregated around the carbon black particles of the GDL. These features became more pronounced for the thicker films. X-ray diffraction confirmed the presence of hexagonal wurtzite ZnO structure on the electrode surface. Electrochemical tests in a 1 cm² flow cell reactor with 1 M KOH electrolyte demonstrated that the ZnO100 (100 ALD cycles) GDE achieved excellent selectivity to carbon monoxide, with a faradaic efficiency of ~90% at -100 mA cm^-2. To assess scalability and long-term performance, the thicker ZnO200 GDE was tested in a 5 cm² membrane electrode assembly with 0.1 M KHCO₃, where it maintained ~90% CO selectivity over 28 hours of continuous operation.

Building on these results, ongoing work aims to develop Cu-based GDEs using ALD with Copper(II) hexafluoroacetylacetonate [Cu(hfac)₂] as a precursor, with the goal of forming multi-carbon products. A supercycle ALD approach is also being explored to fabricate bimetallic  Zinc-Copper catalysts with tailored compositions to improve CO2RR selectivity.

This PhD research is part of the European Union Horizon 2021 MSCA-DN ECOMATES project, which supports the development of selective bimetallic materials and innovative processes for the  efficient electrochemical conversion of CO₂.